The production of fuel grade ethanol from renewable resources is expected to increase. Presently, many bioethanol plants in the U.S. use corn as the feedstock. Fermentation of lignocellulose to produce bioethanol is not currently economical. However, if research on this use of lignocellulose develops successfully, there will be an even larger increase in bioethanol production.
A major drawback to more economical use of bioethanol as a fuel is the energy used to grow the feedstock, to ferment it, and to separate a dry ethanol product from the fermentation broth. In this regard, the development of a lower energy ethanol separation (dehydration) process would be of considerable interest and use to bioethanol producers.
Dehydration of other organic liquids is also of economic importance. Isopropanol is widely used in the electronics industry and in the production of precision metal parts as a drying agent. The component to be dried is dipped or sprayed with anhydrous isopropanol, which removes any water, after which the component is dried. The isopropanol solvent eventually becomes contaminated with water and when it reaches about 10-30% weight of water it must be replaced. It would be economical to recover the isopropanol rather than disposing of it as a hazardous waste, as is presently done. Distillation of isopropanol/water is not economically feasible since it forms an azeotrope at 87% isopropanol-13% water.
Another important organic liquid is acetic acid, the most widely used organic acid. Its primary industrial uses are for the production of vinyl acetate monomer and as a solvent in making terephthalic acid. In production of terephthalic acid, large aqueous acetic acid streams are produced from which acetic acid must be recovered and a water stream produced that is sufficiently decontaminated to be properly discharged into the environment. An energy and cost-saving method for producing a dehydrated acetic acid stream suitable for recycling along with waste water stream suitable for discharging would be of considerable economic interest.
While there are some commercially available membranes capable of dehydrating organic compounds by pervaporation, these membranes are hydrophilic, in that they swell significantly, or even dissolve, in an aqueous environment. They start to lose their separation properties, and are, therefore, unusable, even at water concentrations of just a few percent. The problem is exacerbated if the feed solution is hot. Unfortunately, many economically important organic solutions, such as those mentioned above, are not amenable to treatment by pervaporation for this reason.
There is thus a need in several industrial applications for more economical methods of dehydrating organic/water mixtures.